The Washington University Spectrometry Facility has functioned as a local, regional, national, and international resource for mass spectrometry since 1969 when our first instrument was put into operation. In the intervening years, the facility has grown to include 5 quadrupole GCMS instrument an LCMS instrument, a mass selective detector, a double focusing extended mass range instrument, and an automated isotope ratio system. In the last year, this facility logged 7810 hours of instrument time for actual sample analysis. To our knowledge, we are the only NIH Mass Spectrometry Resource providing routine, high dilution, high precision, dual-inlet dual- collector isotope ratio analyses to the biomedical community. The instrument used for this purpose was purchased with local funds in a "minimal" configuration. Since, at the time, there were no commercially available automated IRMS machines, automation and software control of the instrument was implemented in the facility. Because of initial manufacturer design/construction flaws, this instrument has never functioned within expected specifications an has always been subject to unacceptable "down time". Further, since the individual who developed the hardware and software for this instrument has now let the resource, it has become increasingly more difficult to maintain this "non-standard" instrument in the face of an increasing, heavy sample load. We are asking for support to purchase a current, automated isotope ratio instrument with the manufacturer's data system to allow us to continue to provide IRMS services to the national user's group. In addition, since a) a significant fraction of current development work in human stable isotope tracer kinetics involves precursor- product relationships, b) conventional GCMS is generally not sensitivity enough to measure product isotope enrichments without producing "non-tracer" mass perturbation effects in the precursor pool, and c) IRMS requires difficult sample preparation to obtain the highly pure product required for IRMS isotopic analyses, we are requesting a GC/combustion/IRMS interface to allow facile determination of product isotopic enrichments in biological samples at dilutions higher than those possible by conventional ion monitoring GCMS.